1. Field of the Invention
The present invention relates to a wheel rotating apparatus having a planet gear unit with a high reduction ratio and an in-wheel motor vehicle including the wheel rotating apparatus.
2. Description of the Related Art
There are two types of driving method of in-wheel motor vehicles, namely, a direct drive motor method and a geared motor method.
In the direct drive motor method, an output shaft of a motor is directly coupled to a drive shaft (hub) of a wheel. This method has an advantageous effect in reducing a weight by decreasing the number of parts due to absence of a reducer, but a disadvantageous effect in: a size because the motor becomes large to have a large torque arm; output efficiency; and a dynamic performance.
In the geared motor method, an output of the motor is transmitted to a driving shaft of a wheel after reducing a rotation speed of the motor output. This increases a torque of the motor output with the reducer, improving the dynamic performance by an increased output efficiency with the motor miniaturized. However, the presence of the reducer between the wheel and the motor requires a housing space for the reducer and accessories for supplying oil, resulting in a large size of the apparatus.
In consideration of this, a geared motor method using a planet gear mechanism as a compact reducer is known. JP2849201 and JP2005-81871A disclose such geared methods.
Particularly, JP2005-81871A discloses a technology in which a planet gear reducer, having planet gear members with different diameter gears, is arranged in line with the motor in an axial direction, wherein a break mechanism is disposed on an outer circumferential side of the planet gear with a smaller diameter to efficiently use the space.